Dark Stars, Dark Matter and Black Holes Chris Kouvaris Solvay Inst. Brussels, 5 April 2019
Why Dark Matter Self-Interactions? Problems with Collisionless Cold Dark Matter Core-cusp profile in dwarf galaxies • Diversity Problem • See Hai-Bo Yu’s talk “Too big to fail” • Extra motivation: Provide seeds for the Supermassive Black hole at the center of galaxy Pollack Spergel Steinhardt ‘15 2 2 Numerical Simulations suggest 0.1cm/g< σ /m<1 cm/g
An Alternative to WIMPs: Asymmetric Dark Matter • Asymmetric DM can emerge naturally in theories beyond the SM • Alternative to thermal production • Possible link between baryogenesis and DM relic density TeV WIMP Light WIMP ~GeV n TB = n B M TB = 5GeV e − 4 10 3 ⇤ 18 ⇥ 5 ( 1 × 5 = 5
Asymmetric Dark Stars Can asymmetric dark matter with self-interactions form its own compact objects? • How do they look like? • Can we detect them and distinguish them from NS or BH? • What is the formation mechanism?
Asymmetric Fermionic Dark Stars Tolman-Oppenheimer-Volkoff with Yukawa self-interactions CK, Nielsen ‘15
Asymmetric Bosonic Dark Stars 4 BEC Bosonic DM with λφ Repulsive Interactions: Solve Einstein equation together with the Klein-Gordon Attractive Interactions: We can use the nonrelativistic limit solving the the Gross-Pitaevskii with the Poisson Eby, CK, Nielsen, Wijewardhana ‘15
Asymmetric Bosonic Dark Stars 4
Gravitational Waves from Dark Stars Giudice, McCullough, Urbano ‘16 Observation • Gravitational Waves: • DS+DS->DS or BH • DS+NS-> DS* • DS+BH->BH • Spinning DS
Tidal Deformations of Dark Stars How stars deform in the presence of an external gravitational field? i j V=-(1/2) ε x x ij Q =- λε ij ij λ = Love number Similarly we can estimate the deformation due to rotation
I-Love-Q for Dark Stars Maselli, Pnigouras,Nielsen, CK, Kokkotas, 17 I-Love-Q relations
The Bright Side of Dark Stars Dark Stars could shine via dark Bremsstrahlung if there is e.g. kinetic mixing between the dark and ordinary photon • The luminosity might not be small compared to neutron stars because it is a volume vs surface effect. • The morphology of the spectrum is different from that of a blackbody radiation due to the dependence of the gravitational redshift on the depth of photon production Maselli, CK, Kokkotas… soon
How Asymmetric Dark Stars form? A small fraction of asymmetric SIMP DM interacting via dark photons • Dark Fine Structure Constant should be sufficiently large to deplete antiparticles • Relic dark photons should neither overclose the Universe nor violate BBN constraints of Neff
Formation of Asymmetric Dark Stars ◆ 1 / 2 ✓ π λ > λ J = c s Perturbations grow as long as ρ 0 ( z ) G Chang, Egana-Ugrinovic, Rouven, CK ‘18
Formation of Asymmetric Dark Stars Collapse can proceed via dark photon Bremsstrahlung Cooling
Formation of Asymmetric Dark Stars
Neutron Decay Anomaly and Neutron Star Stability There is a 4 σ discrepancy between bottle and beam experimental measurements of the decay width of neutron. This could be explained if neutron could partially decay to a DM particle Fornal Grinstein ’18. Avoid proton decays However such a scenario leads to significant conversion of neutrons to DM, softening the NS EoS making NS unable to reach 2 M sun. Baym Beck Geltenbort Shelton ’18, Cline Cornell ’18 Adding repulsive DM self-interactions is barely consistent with 2 M sun NS. Cline Cornell ’18, Grinstein Nielsen CK ’18.
Baryon-DM Interactions via the Higgs Portal The Higgs portal induces neutron-DM interactions
Baryon-DM Interactions via the Higgs Portal Energy density chemical equilibrium DM Self-Interactions constraints Constraints from rapid cooling of stars Grinstein Nielsen CK ’18
Converting Neutron Stars to Black Holes Astrophysical black holes produced as the end result of stellar evolution are expected to have masses above 3M sun. Therefore in case of a ~M sun black hole discovery, one would naively expect that it is of primordial origin. This does not have to be the case. Asymmetric DM could implode inside NS converting them to black holes of <3M sun. This can set constraints on DM self- interactions since they dictate how easily asymmetric DM can collapse.
Asymmetric Dark Matter in Neutron Stars Press Spergel ’85, Gould ’86, Capture Nussinov Goldman ’89, CK’07 Thermalization Goldman Nussinov’89, CK Tinyakov ’10 Bertoni Nelson Reddy ’13 Self-Attraction CK Tinyakov Tytgat ’18 Collapse CK Nielsen ’15
Setting New Constraints on Dark Matter Self-Interactions CK Tinyakov Tytgat ‘18
Conclusions Dark Matter Self-Interactions • important to solve CCDM problems Asymmetric Dark Stars • can be probed by gravitational waves • New Dark Stars distinguishable from NS and BH binaries Neutron Decay Anomaly • if this persists, deviation from SM • strong constraints from NS Dark Matter Collapse inside NS • create astrophysical black holes with M<3M sun • new constraints on asymmetric DM and DM self-interactions
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